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Elastic stiffness, acoustic absorption, and photoelastic constants of the crystal have been determined at room temperature using ultrasonic light diffraction and pulse-echo methods. Two acoustic modes have been found to be particularly useful to acousto-optical applications: One is the shear mode propagated in the [110] direction with displacement along [1̄10], which is characterized by a remarkably high acousto-optical figure of merit, M (n6p2/ρv3) = 793×10−18 sec3/g; and the other is the longitudinal mode along [001] with high figure of merit defined taking account of frequency bandwidth, M′ (n7p2/ρv) = 142×10−7 cm2·sec/g, and low acoustic loss.

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All of the elastic stiffness constants except c13 have been found to decrease almost linearly with temperature between −120° and 120°C. The constant c13 reaches the maximum in the vicinity of 0°C, above which it also decreases with temperature. On the other hand, the effective elastic constant (c11–c12)/2, which corresponds to the exceptionally slow shear wave propagating along [110], increases with temperature. The shear wave propagating in the (001) plane making angle of 35.9° with the X axis has zero temperature coefficient of velocity. Acoustic absorptions for several sound modes vary within 1 dB/cm for both the longitudinal wave (measured at 36 MHz) and shear wave (48 MHz) in the measured temperature range. Both real and imaginary parts of the dielectric constants increase monotonically with temperature, while the piezoelectric constant d14 decreases in the temperature range between −150° and 180°C.